/*
 * Copyright 2002-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.http.converter.json;

import java.io.IOException;
import java.lang.reflect.Type;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Map;

import kotlinx.serialization.KSerializer;
import kotlinx.serialization.SerializationException;
import kotlinx.serialization.SerializersKt;
import kotlinx.serialization.json.Json;

import org.springframework.core.GenericTypeResolver;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.http.converter.AbstractGenericHttpMessageConverter;
import org.springframework.http.converter.HttpMessageNotReadableException;
import org.springframework.http.converter.HttpMessageNotWritableException;
import org.springframework.lang.Nullable;
import org.springframework.util.ConcurrentReferenceHashMap;
import org.springframework.util.StreamUtils;

/**
 * Implementation of {@link org.springframework.http.converter.HttpMessageConverter}
 * that can read and write JSON using
 * <a href="https://github.com/Kotlin/kotlinx.serialization">kotlinx.serialization</a>.
 *
 * <p>This converter can be used to bind {@code @Serializable} Kotlin classes.
 * It supports {@code application/json} and {@code application/*+json} with
 * various character sets, {@code UTF-8} being the default.
 *
 * @author Andreas Ahlenstorf
 * @author Sebastien Deleuze
 * @author Juergen Hoeller
 * @since 5.3
 */
public class KotlinSerializationJsonHttpMessageConverter extends AbstractGenericHttpMessageConverter<Object> {

    private static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8;

    private static final Map<Type, KSerializer<Object>> serializerCache = new ConcurrentReferenceHashMap<>();

    private final Json json;


    /**
     * Construct a new {@code KotlinSerializationJsonHttpMessageConverter} with the default configuration.
     */
    public KotlinSerializationJsonHttpMessageConverter() {
        this(Json.Default);
    }

    /**
     * Construct a new {@code KotlinSerializationJsonHttpMessageConverter} with a custom configuration.
     */
    public KotlinSerializationJsonHttpMessageConverter(Json json) {
        super(MediaType.APPLICATION_JSON, new MediaType("application", "*+json"));
        this.json = json;
    }


    @Override
    protected boolean supports(Class<?> clazz) {
        try {
            serializer(clazz);
            return true;
        } catch (Exception ex) {
            return false;
        }
    }

    @Override
    public final Object read(Type type, @Nullable Class<?> contextClass, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException {

        return decode(serializer(GenericTypeResolver.resolveType(type, contextClass)), inputMessage);
    }

    @Override
    protected final Object readInternal(Class<?> clazz, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException {

        return decode(serializer(clazz), inputMessage);
    }

    private Object decode(KSerializer<Object> serializer, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException {

        MediaType contentType = inputMessage.getHeaders().getContentType();
        String jsonText = StreamUtils.copyToString(inputMessage.getBody(), getCharsetToUse(contentType));
        try {
            // TODO Use stream based API when available
            return this.json.decodeFromString(serializer, jsonText);
        } catch (SerializationException ex) {
            throw new HttpMessageNotReadableException("Could not read JSON: " + ex.getMessage(), ex, inputMessage);
        }
    }

    @Override
    protected final void writeInternal(Object object, @Nullable Type type, HttpOutputMessage outputMessage)
            throws IOException, HttpMessageNotWritableException {

        encode(object, serializer(type != null ? type : object.getClass()), outputMessage);
    }

    private void encode(Object object, KSerializer<Object> serializer, HttpOutputMessage outputMessage)
            throws IOException, HttpMessageNotWritableException {

        try {
            String json = this.json.encodeToString(serializer, object);
            MediaType contentType = outputMessage.getHeaders().getContentType();
            outputMessage.getBody().write(json.getBytes(getCharsetToUse(contentType)));
            outputMessage.getBody().flush();
        } catch (IOException ex) {
            throw ex;
        } catch (Exception ex) {
            throw new HttpMessageNotWritableException("Could not write JSON: " + ex.getMessage(), ex);
        }
    }

    private Charset getCharsetToUse(@Nullable MediaType contentType) {
        if (contentType != null && contentType.getCharset() != null) {
            return contentType.getCharset();
        }
        return DEFAULT_CHARSET;
    }

    /**
     * Tries to find a serializer that can marshall or unmarshall instances of the given type
     * using kotlinx.serialization. If no serializer can be found, an exception is thrown.
     * <p>Resolved serializers are cached and cached results are returned on successive calls.
     *
     * @param type the type to find a serializer for
     * @return a resolved serializer for the given type
     * @throws RuntimeException if no serializer supporting the given type can be found
     */
    private KSerializer<Object> serializer(Type type) {
        KSerializer<Object> serializer = serializerCache.get(type);
        if (serializer == null) {
            serializer = SerializersKt.serializer(type);
            serializerCache.put(type, serializer);
        }
        return serializer;
    }

}
